This application claims the benefit of Korean Patent Application No. 2002-31108 filed on Jun. 3, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a radioactive image apparatus, and more particularly, to a radioactive image apparatus which uses radioactive rays to obtain an image of a subject and a method of controlling the focus thereof.
2. Description of the Related Art
Generally, radioactive image apparatuses are used in the medical field to detect abnormal conditions in a human body, and in an industrial field to determine the states of products. In the industrial field, for example, theses apparatuses are used to determine the internal states of the products where it is difficult to disassemble or check whether the products are defective.
FIG. 1 shows a conventional radioactive image apparatus which is used to test products in an industrial field. As shown in FIG. 1, when radioactive rays are irradiated from a radioactive ray generating unit 102 provided above a robot table 104, the radioactive rays pass through a star test pattern 106 mounted on the robot table 104 such that a transmission image 110 of the star test pattern 106 is formed on a radioactive ray detecting unit 108. The star test pattern 106 shown in FIG. 1 is a tool used to measure a focus of the radioactive ray generating unit 102. The star test pattern 106 is a radial arrangement of lead spoke patterns whose thickness becomes thinner toward the center of the radial arrangement.
FIGS. 2A and 2B show transmission images of test patterns obtained by the conventional radioactive image apparatus, in which FIG. 2A shows a satisfactory focus and FIG. 2B shows a dissatisfactory focus. That is, in FIG. 2A, lead spoke patterns are clearly shown in the vicinity of a center of a transmission image. In contrast, in FIG. 2B, lead spoke patterns are not clearly shown in the vicinity of a center of a transmission image.
If the focus is dissatisfactory, it is difficult to obtain a high resolution, and accordingly, the focus must be controlled again. FIG. 3 illustrates a conventional method of controlling a focus of the radioactive image apparatus shown in FIG. 1. First, a star test pattern 106 is mounted on a robot table 104 in operation 302, and a radioactive transmission image 110 is obtained by irradiating radioactive rays onto the star test pattern 106 in operation 304. Next, it is determined, with a naked eye, whether the focus of the radioactive transmission image 110 is satisfactory in operation 306. Where the focus is dissatisfactory, focus-related parameters are corrected in operation 310, and the operation 304 of obtaining the radioactive transmission image is performed again. If a subject has been mounted on the robot table 104, it is removed so as to re-mount the star test pattern 106 for the focus control.
Conditions for determining the resolution of the radioactive image apparatus include the magnitude of the focus of a radioactive source and the focus of an image pickup device which obtains a transmission image. The magnitude of the focus of the radioactive source is dependent on voltages, currents, etc., where an X ray tube is used as the radioactive source. The voltages and the currents should be adjusted frequently depending on the values of matter properties of the subject. In addition, the focus of the image pickup device can be varied by various factors. If some conditions such as the focus of the radioactive source and the focus of the image pickup device are changed, the focus should be controlled again to obtain an optimal resolution. However, in the prior art, naked eyes of the users were used to determine whether the focus was satisfactory. Accordingly, differences among the individuals determining whether the focus was satisfactory were significant, and controlling the focus again required a long period of time.
Accordingly, it is an object of the present invention to provide a radioactive image apparatus having a robot table provided with a jig equipped with various kinds of test patterns, wherein a position of the robot table is adjustable so as to obtain radioactive transmission images of the test patterns. Therefore, the present radioactive image apparatus allows appropriate test patterns to be conveniently used where the focus of the radioactive image apparatus is controlled.
Another object of the present invention is to provide a method of controlling a focus of a radioactive image apparatus, in which a determination of whether the focus is satisfactory is based on a comparison between deviations of pixel values of radioactive transmission images of test patterns and an adjustment of resolution-related parameters. The determination and adjustment operations are automatically performed in association with a computer of the radioactive image apparatus. Accordingly, the focus of the radioactive image apparatus is controlled with a very high accuracy as compared to a conventional focus control performed by a naked eye.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a radioactive image apparatus comprising a radioactive ray generating unit which irradiates radioactive rays onto a subject, an adjustable robot table having a subject fixing member which holds the subject, and a test pattern mounting member, wherein a position of the adjustable robot table is changeable to have the radioactive rays irradiated onto the subject, and a radioactive ray detecting unit which produces a radioactive transmission image formed by irradiating the radioactive rays onto the subject.
To achieve the above and other objects of the present invention, there is also provided a method of controlling a focus of a radioactive image apparatus having a radioactive ray generating unit which generates radioactive rays onto a subject, an adjustable robot table which includes a subject fixing member for positioning the subject and a test pattern mounting member for receiving one or more test patterns, and a radioactive ray detecting unit which produces a radioactive transmission image formed by irradiating the radioactive rays onto the subject, the method comprising obtaining a radioactive transmission image of the test pattern, defining a circle with a given radius in the radioactive transmission image of the test pattern, detecting values of pixels located on a circumference of the circle, calculating a standard deviation of the values of the pixels located on the circumference of the circle, and determining the radius of the circle to be an index factor of a resolution in response to the standard deviation being smaller than a preset threshold value.